1. Field of the Invention
The present invention relates to a wireless transceiver system using Multi Carrier modulation and, in particular, to a Multi Carrier transceiver which can reduce a transmission bandwidth to one half of required bandwidth by using a symmetry of discrete Fourier transformed signal and a method thereof.
2. Information Disclosure Statement
In general, a high speed wireless transmission mainly uses a Direct-Sequence Spectrum Spread Method, a frequency hopping method or a Multi Carrier transmission method.
With reference to FIGS. 1 and 2, a basic concept of multi carrier modulation method used in the multi carrier transmission method is described.
FIG. 1 illustrates a basic transmission structure of the multi carrier modulation method having N subcarriers.
The basic concept of the multi carrier modulation method is to transmit by dividing an available frequency into several subchannels. These subchannels orthogonally overlap each other.
When a symbol interval is taken as T, the interval xcex94f between the subcarriers which can assure the orthogonality is a multiple of k/T (k is an integer).
FIG. 2 shows a signal spectrum of multi carrier modulation method.
The system of FIGS. 1 and 2 can be analyzed by an equation 1.                                                                         s                ⁡                                  (                  t                  )                                            =                              xe2x80x83                            ⁢                                                ∑                                      k                    =                    0                                                        n                    -                    1                                                  ⁢                                  xe2x80x83                                ⁢                                                      X                    k                                    ⁢                                      cos                    ⁡                                          (                                                                        2                          ⁢                          π                          ⁢                                                      xe2x80x83                                                    ⁢                                                      f                            c                                                    ⁢                          t                                                +                                                  2                          ⁢                          π                          ⁢                                                      xe2x80x83                                                    ⁢                          k                          ⁢                                                      xe2x80x83                                                    ⁢                          Δ                          ⁢                                                      xe2x80x83                                                    ⁢                          ft                                                                    )                                                                                                                                              =                              xe2x80x83                            ⁢                                                                    ∑                                          k                      =                      0                                                              N                      -                      1                                                        ⁢                                      xe2x80x83                                    ⁢                                                            X                      k                                        ⁢                    cos                    ⁢                                          xe2x80x83                                        ⁢                    2                    ⁢                                          xe2x80x83                                        ⁢                    π                    ⁢                                          xe2x80x83                                        ⁢                                          f                      c                                        ⁢                    t                    ⁢                                          xe2x80x83                                        ⁢                    cos                    ⁢                                          xe2x80x83                                        ⁢                    2                    ⁢                    π                    ⁢                                          k                      T                                        ⁢                    t                                                  -                                                      ∑                                          k                      =                      0                                                              N                      -                      1                                                        ⁢                                      xe2x80x83                                    ⁢                                                            X                      k                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                    2                    ⁢                    π                    ⁢                                          xe2x80x83                                        ⁢                                          f                      c                                        ⁢                    t                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                    2                    ⁢                                          xe2x80x83                                        ⁢                    π                    ⁢                                          k                      T                                        ⁢                    t                                                                                                                          =                              xe2x80x83                            ⁢                                                                                          m                      l                                        ⁡                                          (                      t                      )                                                        ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                  2                  ⁢                                      xe2x80x83                                    ⁢                  π                  ⁢                                      xe2x80x83                                    ⁢                                      f                    c                                    ⁢                  t                                -                                                                            m                      q                                        ⁡                                          (                      t                      )                                                        ⁢                  sin                  ⁢                                      xe2x80x83                                    ⁢                  2                  ⁢                                      xe2x80x83                                    ⁢                  π                  ⁢                                      xe2x80x83                                    ⁢                                      f                    c                                    ⁢                  t                                                                                                                                          m                  l                                ⁡                                  (                  t                  )                                            =                              xe2x80x83                            ⁢                                                ∑                                      k                    =                    0                                                        N                    -                    1                                                  ⁢                                  xe2x80x83                                ⁢                                                      X                    k                                    ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                  2                  ⁢                                      xe2x80x83                                    ⁢                  π                  ⁢                                      k                    T                                    ⁢                  t                                                                                                                                          m                  q                                ⁡                                  (                  t                  )                                            =                              xe2x80x83                            ⁢                                                ∑                                      k                    =                    0                                                        N                    -                    1                                                  ⁢                                  xe2x80x83                                ⁢                                                      X                    k                                    ⁢                  sin                  ⁢                                      xe2x80x83                                    ⁢                  2                  ⁢                                      xe2x80x83                                    ⁢                  π                  ⁢                                      k                    T                                    ⁢                  t                                                                                        [                  Equation          ⁢                      xe2x80x83                    ⁢          1                ]            
In equation 1, it can be known that s(t) is in form obtained by modulating baseband signals mI(t) and mg(t) with a frequency fc. Defining t=nT/N in the baseband signals mI(t) and mg(t), a discrete signal form of the base band signals is obtained.                                                         m              l                        ⁡                          (              n              )                                =                                    ∑                              k                =                0                                            N                -                1                                      ⁢                          xe2x80x83                        ⁢                                          X                k                            ⁢              cos              ⁢                              xe2x80x83                            ⁢              2              ⁢              π              ⁢                              nk                N                                                    ⁢                  
                ⁢                                            m              q                        ⁡                          (              n              )                                =                                    ∑                              k                =                0                                            N                -                1                                      ⁢                          xe2x80x83                        ⁢                                          X                k                            ⁢              sin              ⁢                              xe2x80x83                            ⁢              2              ⁢                              xe2x80x83                            ⁢              π              ⁢                              nk                N                                                                        [                  Equation          ⁢                      xe2x80x83                    ⁢          2                ]            
It can be seen that the equation 2 is a same representation as an N point Inverse Discrete Fourier Transform (IDFT) with the exception of a scaling factor 1/N and j of imaginary term. Therefore, the baseband signal can be implemented by carrying out the IDFT of a symbol to be transmitted, and the same result can be obtained by dividing the result of IDFT into real terms and imaginary terms, transforming the discrete signal into a continuous signal, modulating the result with the frequency fc and carrying out a sum operation thereof. At this time, it should be noted the (xe2x88x92) sign must be put in sum operation of imaginary parts. The Discrete Fourier Transform (DFT) block can be further fast calculated by using a fast Fourier transform (FFT) digital signal processor (DSP). A construction of a Multi Carrier wireless transceiver of Orthogonal Frequency Division Multiplexing (OFDM) method based on the FFT is shown in FIG. 3.
FIG. 3 is an illustrative construction drawing of a conventional Multi Carrier wireless transceiver which comprises a serial/parallel (S/P) conversion section 111, an Inverse Fast Fourier transformation section (IFFT) 112, a parallel/serial (P/S) transformation section 113, a digital/analog (D/A) conversion section 114, a modulation section 115, a phase shift section 116, a synthesizing section 117, a transceiving channel 118, a demodulation section 119, a phase shift section 120, a low pass filter 121, an analog/digital (A/D) conversion section 122, a serial/parallel conversion section 123, a Fast Fourier Transformation section (FFT) 124 and a parallel/serial conversion section 125.
A description of operation of the conventional Multi Carrier wireless transceiver having a structure described above is given below.
The serial/parallel conversion section 111 converts the transmission data into N low speed parallel binary data and transmits the converted data to the IFFT section 112.
The IFFT section 112 inverse Fourier transforms the input data by taking the input data as frequency domain spectrum components and transmits to the parallel/serial conversion section 113 an output composed of a real part data sequence and an imaginary part data sequence.
The parallel/serial conversion section 113 divides the Inverse Fourier transformed parallel data into a real part and imaginary part, inserts a guard bit for preventing an adjacent signal interference in a transmitting channel, converts the parallel data into a serial data sequence and transmits it to the digital/analog conversion section 114. At this time, the output is divided into a real part (Re) data and imaginary part (Im) data. The digital/analog conversion section 114 converts an input Multi-level digital signal into analog signal and transmits the converted signal to the modulation section 115. The modulation section 115 multiplies the input analog signals with a carrier of cos 2xcfx80 fct and a carrier obtained by shifting the phase of the former carrier by 90 degree by the phase shift section 116, respectively. The synthesizing section 117 inverts the sign of the imaginary part signal from the modulation section 115, adds the imaginary part signal to the real part signal, and transmits the added signal through the channel 118.
The demodulation section 119 divides the received signal from the channel 118, restores the divided signals to signals same as the output signals from the digital/analog conversion section 114 by multiplying the divided signals with a signal of cos 2xcfx80 fct having same frequency and phase as the carrier and a signal obtained by shifting the phase by 90 degree by the phase shift section 120, respectively, and transmits them to low pass filters 121. The low pass filters 121 only passes low frequency band among the demodulated signals, and the analog/digital conversion section 122 converts the analog signal transmitted from the low pass filters 121 into digital and transmits it to the serial/parallel conversion section 123.
The serial/parallel conversion section 123 converts the input real part signal and inverted imaginary part signal into N low speed parallel binary data, removes the guard bit and transmits the data to the FFT section 124. The FFT section 124 discrete Fourier transforms the input discrete parallel data and transmits the data to the parallel/serial conversion section 125, and the parallel/serial conversion section 125 converts the Fourier transformed parallel data into serial data stream.
FIG. 4 is a wireless channel frequency spectrum diagram in which the signal transmitted from the conventional Multi Carrier wireless transceiver is presented in a frequency spectrum at the channel.
As shown in FIG. 4, the conventional Multi Carrier wireless transceiver occupies a bandwidth of (N+1)xcex94f, where the xcex94f is the carrier interval.
As shown in FIG. 4, in case of using the conventional Multi Carrier wireless transceiver, since the occupied bandwidth at the wireless or wired channel is large, there are problems that degrades transmission efficiency and is vulnerable to multi-path fading, noise and interference.
An object of the present invention invented to solve the problems described above is to provide a Multi Carrier wireless transceiver and a method thereof which can reduce the transmission bandwidth to one half of required bandwidth by using the symmetry of the discrete Fourier transformed signal in a wireless transceiver system.
A reduced bandwidth Multi Carrier wireless transceiver of the present invention to accomplish the object described above comprises: a first serial/parallel conversion means for converting externally input serial signals into parallel signals; an Inverse Fast Fourier Transform (IFFT) means for Inverse Fourier Transforming the plurality of parallel signals transmitted from the first serial/parallel conversion means, dividing the signals into data sequences of real part and imaginary part, and outputting the signals by reducing the number of channels; a transmission processing means for converting the output signal of the IFFT means into analog signal and transmitting a modulated signal; a reception processing means for demodulating the signal transmitted from the transmission processing means and thereafter converting the demodulated signal into digital signal; a high frequency signal generation means for receiving the output signal of the reception processing means and recovering the high frequency signal; and a signal recovery means for receiving the output signal of the high frequency signal generation means and outputting the original serial data.
A reduced bandwidth Multi Carrier wireless transceiving method which can reduce transmission bandwidth to a half of required bandwidth by using the symmetry of Inverse Fourier Transformed signal comprises the steps of: a first step in which a serial/parallel conversion section converts externally input serial signals into parallel signals; a second step in which an Inverse Fast Fourier Transform (IFFT) section Inverse Fourier Transforms the plurality of parallel signals transmitted from the first serial/parallel conversion means, divides the signals into data sequences of real part and imaginary part, and outputs the signals by reducing the number of high frequency channels; a third step in which a transmission processing section converts the output signal of the IFFT section into analog signal and transmits the signal by modulating the signal; a fourth step in which a reception processing section demodulates the signal transmitted from the transmission processing means and thereafter converts the demodulated signal into digital signal; a fifth step in which a high frequency signal generation section receives the output signal of the reception processing means and generates the high frequency signal; and a sixth step in which a signal recovery section receives the output signal of the high frequency signal generation means and outputs the original serial data.